Fundamental study on environmental stress cracking effects in polymer nanocomposites

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Environmental stress cracking (ESC) is one of the most common reasons of lifetime shortening for plastic components. The risk of ESC always occurs when the product is subject to the simultaneous effects of mechanical stresses and aggressive fluids that trigger stress cracking. The consequences of the premature failure are often serious and can be life-threatening when the product is used for instance in the medical care. Accordingly, this is considered to be a great challenge to understand fundamentally and based on this to improve the ESC resistance of polymeric materials. Generally, the ESC resistance improves with increasing molecular weight and a broad molecular weight distribution of the polymer matrix. Moreover, the notable preliminary results reveal that the incorporation of nanofillers provides new possibilities to improve the ESC resistance and consequently prolong the service lifetime of the polymers.Therefore, the objectives of this research proposal are to gain a deep understanding of the influence of nanofiller parameters and the molecular parameters on the ESC behavior of the amorphous polymer under various environment conditions (stress cracking agents and ambient temperatures) as well as different challenging mechanical conditions (static and dynamic loading). Polymethylmethacrylate (PMMA) with different molecular weights and molecular weight distributions will be used as polymer matrices. The PMMA will be compounded with different types, sizes, and contents of nanofillers which have spherical (nano-silicon dioxide (SiO2)), rod-like (halloysite nanotubes (HNTs)) as well as platelet-like geometries (commercial and special surface treated layered silicates). By utilizing mechanical, thermal, morphological, optical, rheological, and surface tension analysis methods, it will be possible to correlate the structure-properties relationship of the nanocomposites. The received insights of this analysis will be the key to understanding the ESC behavior of the polymer nanocomposites.